Conventional overhead lift cranes include at least one bottom block that, in combination with a trolley hoist assembly having a hoist drum, raise and lower a load hook or other lifting mechanism attached to the bottom block. Each bottom block with its attached load hook is designed to handle a certain maximum load. Each bottom block typically includes a pair of sheaves with two ropes reeved between the pair of sheaves and the hoist assembly so that each sheave is supported by a single one of the two ropes. In this configuration, if one of the two ropes breaks, any load attached to the hook moves in an uncontrolled manner and does not remain level.
One prior solution to solve this problem uses four ropes to support the bottom block. If any one of the four ropes breaks, the bottom block remains level even with a full load attached to the hook. However, four ropes occupy a larger portion of a hoist drum. Thus, a larger hoist drum is required which increases the trolley spread and the overall weight of the trolley hoist assembly.
There is a need in the industry to provide lift cranes that are single failure proof. There is also a never ending need in the industry to provide lift cranes of reduced size and weight without sacrificing lift capabilities. Accordingly, there is a need in the art for an improved a bottom block assembly for use with a lift crane.